Two-unit zoom lens system and image pickup apparatus using the same

Abstract

A two-unit zoom lens system includes in order from an object side thereof, a first lens unit G 1 having a negative refracting power, a second lens unit G 2 having a positive refracting power, and an aperture stop which is disposed between the first lens unit G 1 and the second lens unit G 2 , and which moves integrally with the second lens unit. At a time of zooming from a wide angle end to a telephoto end, a distance between the first lens unit G 1 and the second lens unit G 2 is narrowed. At the time of zooming from the wide angle end to the telephoto end, the first lens unit G 1 , after moving toward an image side, moves toward an object side. At the time of zooming from the wide angle end to the telephoto end, the second lens unit G 2 moves toward the object side. The second lens unit G 2 includes in order from the object side thereof, a front sub-unit having a positive refracting power, and a rear sub-unit having a negative refracting power. The two-unit zoom lens system satisfies predetermined conditional expressions.

1. A two-unit zoom lens system comprising in order from an object side thereof:
 a first lens unit having a negative refracting power; 
 a second lens unit having a positive refracting power; and 
 an aperture stop which is disposed between the first lens unit and the second lens unit, and which moves integrally with the second lens unit, wherein 
 at a time of zooming from a wide angle end to a telephoto end, a distance between the first lens unit and the second lens unit is narrowed, and 
 at the time of zooming from the wide angle end to the telephoto end, the first lens unit, after moving toward an image side, moves toward an object side, and 
 at the time of zooming from the wide angle end to the telephoto end, the second lens unit moves toward the object side, and 
 the second lens unit comprises in order from the object side thereof, a front sub-unit having a positive refracting power and a rear sub-unit having a negative refracting power, with the longest air space in the second lens unit between the front sub-unit and the rear sub-unit, and there is no other lens unit in the second lens unit, and 
 the two-unit zoom lens system satisfies the following conditional expressions
     f   t   /f   w >3.6  (1) 
   0.5 <d   2FR   /f   w <1.5  (2) 
 
 where, 
 f w  denotes a focal length at the wide angle end, of the two-unit zoom lens system, 
 f t  denotes a focal length at the telephoto end, of the two-unit zoom lens system, and 
 d 2FR  denotes an air space on an optical axis between the front sub-unit and the rear sub-unit in the second lens unit. 
 
   
   
     2. The two-unit zoom lens system according to  claim 1 , wherein a focusing from an object at a long distance to an object a short distance is carried out by moving the rear sub-unit in the second lens unit to the image side. 
   
   
     3. The two-unit zoom lens system according to  claim 1 , wherein the two-unit zoom lens system satisfies the following conditional expressions
   3 <D   w   /f   w <8  (3) 
   0.3 <D   t   /f   t <1.8  (4) 
 where, 
 D w  denotes an overall optical axial length at the wide angle end, of the two-unit zoom lens system, 
 D t  denotes an overall optical axial length at the telephoto end, of the two-unit zoom lens system, and 
 the overall length is a length which is obtained by adding a back focus expressed in terms of an air conversion length, to an optical axial thickness from a surface of incidence of a lens nearest to the object up to a surface of emergence of a lens nearest to the image, of the two-unit zoom lens system. 
 
   
   
     4. The two-unit zoom lens system according to  claim 1 , wherein the first lens unit comprises a negative lens which is disposed nearest to the object, and which satisfies the following conditional expression
   0.0<( r   L11   +r   L12 )/( r   L11   −r   L12 )<3.0  (5) 
 where, 
 r L11  denotes a paraxial radius of curvature of a surface on the object side, of the negative lens nearest to the object, in the first lens unit, and 
 r L12  denotes a paraxial radius of curvature of a surface on the image side, of the negative lens nearest to the object, in the first lens unit. 
 
   
   
     5. The two-unit zoom lens system according to  claim 1 , wherein
 the front sub-unit in the second lens unit comprises a cemented lens component having a positive lens and a negative lens, and 
 an Abbe's number of the negative lens in the cemented lens component is smaller than an Abbe's number of the positive lens in the cemented lens component. 
 
   
   
     6. The two-unit zoom lens system according to  claim 1 , wherein the total number of lenses in the rear sub-unit in the second lens unit is one. 
   
   
     7. The two-unit zoom lens system according to  claim 1 , wherein a lens surface nearest to the object and a lens surface nearest to the image in the front sub-unit in the second lens unit are aspheric surfaces. 
   
   
     8. An image pickup apparatus comprising:
 a two-unit zoom lens system; and 
 an image pickup element which is disposed at an image side of the two-unit zoom lens system, and which converts an optical image formed by the two-unit zoom lens system, to an electric signal, wherein 
 the two-unit zoom lens system is a zoom lens system according to  claim 1 . 
 
   
   
     9. The image pickup apparatus according to  claim 8 , further comprising:
 an image conversion section which converts the electric signal including a distortion due to the two-unit zoom lens system, to an image signal in which, the distortion is corrected by an image processing. 
 
   
   
     10. The image pickup apparatus according to  claim 8 , wherein
 in a state at the wide angle end of the two-unit zoom lens system, an angle formed between an optical axis and a chief ray which is emerged from the two-unit zoom lens system directed toward a maximum image height of an effective image pickup area of the image pickup element satisfies the following conditional expression
   −40°< EX ( w )<−11°  (6) 
 
 where, 
 EX(w) denotes the angle formed between the optical axis and the chief ray which is emerged from the two-unit zoom lens system directed toward the maximum image height of the effective image pickup area of the image pickup element.